As soon as Shannon, a duchess, sees Silvasta, her brother-in-law by her mother's remarriage, she remembers her previous life. In the novel “The Black Knight and the Praying Princess,” she finds herself in a world where her sister-in-law, Shannon Tia Freuline, is cruelly killed by the worst hero, Silvasta. Shannon runs away from Silvasta, who shows her tyrannical nature even at a young age by glaring at her and pushing her away as soon as she meets her. However, Shannon discovers Silva's true self by chance... A love romance between a tyrant brother-in-law and a reincarnated sister-in-law!